Metastasis of malignant tumors is positioned as the terminal phase in the process of progress of tumors, which is a malignant phenotype that leads the patients to death. At present, chemotherapy agents are mainly used for inhibiting metastasis accompanied by enucleation of tumors. However, satisfactory results are not always obtained. Thus, development of an antimetastasis agent having high effectiveness is desired.
Recently, it was reported that prostaglandin I.sub.2 (PGI.sub.2) and the like are effective against hematogenous metastasis of mouse tumors (see Science, Vol. 212, 1270, (1981)). However, these compounds are unstable so that they cannot be systemically administered as pharmaceuticals.